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Allosaurus
Allosaurus was a genus of large theropod dinosaur native to North America in the Jurassic period. It is the type genus of the infraorder Carnosauria, the superfamily Allosauroidea, and the family Allosauridae. In other words, Allosaurus is the standard by which other carnosaurs are defined. Its closest relative was probably Antrodemus; many of the genera in the family Allosauridae are thought to be possible synonyms of Allosaurus, the most notable of which being Epanterias, which seems nearly identical to Allosaurus, albeit slightly larger. Allosaurus, along with the unrelated Tyrannosaurus, is one of the best-known theropods. It has been featured in many books and films, and is probably the second-most popular theropod among the general public, after Tyrannosaurus. Discovery & Fossil Record The first described fossil in this history was a bone obtained secondhand by Ferdinand Vandiveer Hayden in 1869. It came from Middle Park, near Granby, Colorado, probably from Morrison Formation rocks. The locals had identified such bones as "petrified horse hoofs". Hayden sent his specimen to Joseph Leidy, who identified it as half of a tail vertebra, and tentatively assigned it to the European dinosaur genus Poekilopleuron as Poicilopleuron valens. He later decided it deserved its own genus, Antrodemus. Allosaurus itself is based on YPM 1930, a small collection of fragmentary bones including parts of three vertebrae, a rib fragment, a tooth, a toe bone, and the shaft of the right humerus. Othniel Charles Marsh gave these remains the formal name Allosaurus fragilis in 1877. Allosaurus comes from the Greek allos/αλλος, meaning "strange" or "different" and saurus/σαυρος, meaning "lizard" or "reptile". It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery. The species epithet fragilis is Latin for "fragile", referring to lightening features in the vertebrae. The bones were collected from the Morrison Formation of Garden Park, north of Cañon City. At the Cleveland Lloyd Dinosaur Quarry in Emery County, Utah sporadic work had taken place as early as 1927, but major operations did not begin there until 1960. Under a cooperative effort involving nearly 40 institutions, thousands of bones were recovered between 1960 and 1965. It is notable for the predominance of Allosaurus remains, the condition of the specimens, and the lack of scientific resolution on how it came to be. Majority of bones belong to about 46 Allosaurus fragilis, and the fossils found there are disarticulated and well-mixed. Nearly a dozen scientific papers have been written on the taphonomy of the site, suggesting numerous mutually-exclusive explanations for how it may have formed. Suggestions have ranged from animals getting stuck in a bog, to becoming trapped in deep mud, to falling victim to drought-induced mortality around a waterhole, to getting trapped in a spring-fed pond or seep.[47] Regardless of the actual cause, the great quantity of well-preserved Allosaurus remains has allowed this genus to be known in detail, making it among the best-known theropods. Skeletal remains from the quarry pertain to individuals of almost all ages and sizes.